A Comparative Study of Single-phase Non-isolated Bidirectional dc-dc Converters Suitability for Energy Storage Application in a dc Microgrid
Polycarp Odo
Abstract
Off-grid electricity provision in rural areas where extension of grid is impossible has seen a tremendous research in solar home systems and Islanded DC microgrid design. DC microgrid design has come in many forms, but the most interesting topologies are those that provide power sharing among distributed generators through equalization of state of charge of multiple BESS architecture in both charging and discharging mode. This is mostly implemented using droop control. Of importance in microgrid design is bidirectional DC-DC converters interfacing the BESSs with the DC Bus. Non-isolated bidirectional DC-DC converters are used when galvanic isolation and high-step up or step-down of voltage is not required as against isolated converters. This is commonly implemented using bidirectional buck-boost (half bridge) converters to ensure power flow both in and out of the BESS. This study carries out a comparative study of other single-phase non-isolated bidirectional converters suitability in DC microgrid design with respect to multiple BESS storage architecture for redundancy. The converters considered are buck-boost, Cascaded buck-boost, SEPIC and buck-boost with tapped inductor. They were operated under the same condition and compared using the following headings: SoC discharge rate, amount of discharge current, DC Bus voltage regulation, their capability and number of active and passive elements used. The cascaded half bridge shows the highest discharge current.